They have posted the rules for them on their site. I’ll be doing a write-up on those rules later today or tomorrow morning, so stay tuned.

Here’s Forge World’s official blurb…

Deployed onto the battlefield as elite shock troops or the bodyguards of their magos overseers, Mechanicum Scyllax Guardian-automata have been adapted with a wide variety of mechadendrites and servo-arms for dissecting living matter with murderous speed. With an armoured carapace as durable as Legiones Astartes battle plate and powered by a rad furnace which can vent debilitating radiation at will, the Scyllax Guardian-automata are a force to be truly feared on the battlefield.

The Mechanicum Scyllax Guardian-automata Covenant consists of four Scyllax Guardian-automata, each armed with a Scyllax bolter and various interchangeable claws and mechadendrites forming a mechadendrite combat array. Scyllax Guardian-automata Covenants can be taken in Mechanicum armies in Horus Heresy games and experimental rules for this unit are available to download here.